Pulse generator



July 29, 1952 A. H. FREDRICK 7 2,605,422

' PULSE GENERATOR F'iled Nov. 26, 1945 I (VARIABLE I i I 3''! i qINVENTOR TIME ARDEN H. FREDERICK BYW ATTORNEY I circuits.

Patented July 29, 1952 PULSE GENERATOR Arden H. Fredrick, Boston, Mass.,assignor, by mesne assignments, to the United States of America asrepresented by the Secretary of th Navy Application November 26, 1945,Serial No. 630,940

7 v 12 Claims.

This invention relates to a circuit for producing short-duration markingpulses and, more particularly, to a circuit for producing two series ofmarking pulses, one series of which is variable in time phase withrespect to the other series.

One conventional type'of marking pulse generator includes afrequency-stabilized oscillator which controls the repetition rate of amultivibrator or sawtooth generator followed by differentiating andclipping circuits to shape the wave thus produced to theform required'bythe markingv pulse.- A disadvantage of this type of generator is theadded complexity of these shaping Another ,conventionalltype of marking"pulse generator includes Ta frequency stabiliz'ed oscillator having acurrent difierentiating choke in the cathode circuit-"Disadvantages ofthis type of generator are that the output pulses, if taken from thecathode circuit, are broad and of small amplitude, and if taken from theplate circuit are diflicult to use because of the high impedance acrossthe output terminals.

It is an object of this inventionto provide a m'arking'pulse generatorwhich does not require complex shaping circuits.

It is a further o ject of this:invention to provide a marking pulsegenerator which produces narrow pulses having high'amplitude.

It is a further object of this invention'to projvide a marking pulsegenerator which is" frequency-stabilized by a piezo-electric crystal.

It is a further object of this invention to provide a marking pulsegenerator which "produces two'seri'es of' marking. pulses, thepulses ofone series being adjustable'in'time phase with respect to the pulses ofthe other series. These and other obj ects will be more apparent uponconsideration of. the following description together with theaccompanying drawing in which:

'. Fig; 1 is a circuitdiag'ram' of an embodiment I of the invention; and

Fig. 2 is a. graphical: representation of certain wave forms which'occu'rin the embodiment of Fig.1;

, specifically, with reference t th embodiment of this invention shownschematically in Fig. 1,

'the'circuit comprises an oscillator tube III fre- "quency-stabilized'bya piezo-electric crystal l2 Iac'ed in the grid-cathode circuit. 'rn loadim-' pedance for theoscillator tube is provided by the tuned primary oftransformer 32 with its coupled impedance, iand 'by' thefcathod e;resistor 13 1 tans se mente ir it sent e tion at the resonant frequencyof the frequencystabilizing element is provided by capacitor 16 inparallel with the grid-plate capacitance of the 0scillator tube.Oscillation is initiated by some transient impulse in the usual mannerand continues at a frequency determined principally by thecharacteristics of the piezo-electric crystal. During a part of: thecycle of oscillation, the grid of tube I0 is driven positive withrespect to the cathode, causing grid current to flow through resistor lI. The voltage drop across resistor I I due to this flow of grid currentproduces a negative bias voltage on the grid oftube II), which ismaintained by the stray capacitance of the grid circuit to ground.Becauseof the negative bias thus produced, grid current is permitted toflow during only a portion of the positive one-half cycle of alternatinggrid voltage. Likewise the time of flow of total space current islimited to some fraction of one-half cycle, resulting in periodic spacecurrent pulses as shown in waveform B of Fig. 2. These space currentpulses, flowing through resistor I3, produce a voltage drop across thisresistor. This voltage drop is impressed across the primary of theauto-transformer I5 through a direct current blocking capacitor l lcausing a current to flow in the auto-transformer IS in response to thediscontinuities of the space current pulses as shown in waveform C ofFig. 2.

plifier tube 20 and ground through' the direct current blockingcapacitor I8; Tube 20 is supplied with a negative grid bias throughresistor 2!, so adjusted th'at'the operating point of tube 20 is nearplate current cutoff in the non-linear region. of its grid voltage.versus plate current characteristics. A negative voltage pulse appliedto the grid of tubefiil causes .very little change in space current,because of the operating point chosen. A positive voltage pulse,however, causes a suddent increase in the space current flowing throughresistors 22 and 24. The voltage drop thus produced across resistor 24(between terminal 34 'and ground), a$jhQWIl in waveform D thisembodiment through the distributed capaci-.

tance of the piezo-electric crystal holder shield 31.

i This positive feed-back of energy at the pulse frequency effectivelyincreases the ampli tude of the pulse during its iorrnatio'n bypartially neutralizing the efiectsjofdegeneration due to the cathodeload impedance. 7

A sinusoidal voltage, alternating at a frequency determined by thepiezo-electrlc crystal, is developed across the parallel-resonantimpedance formed by the primary of transformer 32 and capacitor 33 asshown in waveform A 'of Fig, A fundamentalcondition of operation is thatthis ifnpedance appears as an inductive reactance at, the'operatingfreduency of the crystal. The secone yor transformer '32 istuned by means of capacitor 2 5. The time -phase of the secondaryvoltage with respect to the primary voltage can-be varied by tuning thesecondary o'ftransformer fl with capacitor '25 so that it ispara11e1+resonamat a higher or lower frequency than that of the primaryvoltage. An additional lagging phase Shift is introduced by resistor [TIand the secondary tuned circuitre- 'actance, so that the phase of thesecondary voltage may be adjusteli to lag the primary voltage by thedesired amount; I V

The variable phas'e sinusoidal voltage thus produced is impressedbetween the grid of tube 30 and ground. The voltage drop produced by thespace current of tube -'30 flowing through resistor 21 'causes thecathode of tube 30 to be *at a positive potential with respect to'th'egrid, placing the operating point in the non-linear region of the grid,voltage versus plate current characteristic of j-the 'tiibe "very nearplate current cut-off. During that part fof the' grid voltagelcycle whenthe grid "is negative with respect to the cathode, the plate current i'sreduced to z i s rene al-l h n ei *efir 'in the pr maler auto-transforrner 2 9 During the'positive one-halt clycle howjever, thespace curre'ntpf tube 30,]flowing-through the primary ofauto-transformer19 is 'suddenlyincreased. A voltage is 'induced n the secondary which isproportional to the 'rate oi change ol: the primary current withrespectto time. The value of resistor 3| is so chosenjthat theparallelresonant impedance formed jby the "self-inductance ofauto-transformer 29 "and distributed circuit reactance "iscritically'damped The voltage drop across r'sistortl (between terminal36 and ground), as shown in waveformE of Fig. 2, is used as thevariablejtime=phase positive marking pulse output to produce at terminal36 a series of pulsesfvari able in time phase with respect to the seriesof pulses at terminal 34.

secondary of auto-transformer f5 and between ground and the secondaryo'f auto-transformer '29. In this case the values of resistors [9,21,

' i 'electt n t a, t

and 3| can be chosemto provide proper grid,

"o markin pu s; s id e erat critical damping of the resonant circuitoscillations.

The invention is only to be limited by the appended claims.

What is claimed is:

1. A generatorfor producing a. series of pairs of marking pulses, thetimfespacing of said pairs being variable, said generator comprising, anoscillator circuit including an electron tube, a tuned anode circuit, acathode circuit and a positive feedback circuit coupled between saidanode circuit and the grid-cathode circuit of said electron tubathecurrent in said cathode circu'it comprising a, series of recurrentpulses, an auto-transformer coupled to said cathode circuit, criticaldamping means connected in shunt with the output of said'auto-transfonner, amplifying means coupled to said auto-transformeradapted to amplify only positive pulses in the output thereof therebytoproducea first pulsegin each of a r i s, P ase ph ls 'ifi 'a sc pl j t ad n d wedsiv a t. second am i e mse s le o Sa hes 'sh ffin 'm en sa iie' bir amplifier being so 'bia'sedjthat the anode current thereincomprises a series of recurrent pulses occurring in a predeterminedtimefrelationship to the signal 'couplfed fromsaid phase shiftingeans,saidsecond amp r' including a second u or n fo ,in. h out u .ther qjifo amplifying said series of fanode "current pulses in said secondamplifie "he outpu't sigrial 'oi" "said-second "auto tran er being ascena pulse in each of said pairs. I

2. A generator, as in claim l, wherein said phase shiftingineans isadjustable to vary the time s i .b ee 'puls si n Said, Pa -l V 3- nrawtasin i W1 9 j oscillator ircuitjincludes'a piezo 'electric crystaltocontrol the frequencythereo'f. W 4. A een m as n new mar a electrontube in said oscillator circuit includes a control grid, said generatorfurtherfccmprising a piezoelectric crystal -con'nec "d betweenthecathode and control grid ofsaid electron tube and feedback means fromamplifying meansv to the tube in said oscilla "r 5; A generator V-lfor p(1H9 of marking pulses, 's'a an oscillator circuit inc a tuned "anodeC11: 7 p i i ed aq j rcm ano e. c rcuit fen .it

said e e t on tub e e I V f dpairs, phase shiftingfmeans'coupled to saidtuned anode circuit, and pulse generating amplifier means coupled to,saidphase shiftingffii'ean's, said pulse generating amplifier meansproducing a se o rpu ses n, pred srmm dtiniere at o ship to thesignalifrom said'phase shi'f ing means,

said last-mentionedseries"of pulses comprising a second pulse in each ofsaid pairs. l.

.6- Alsefi ra qr'i ip od ic i sf an, oscillator circuit 'incfudrng atune e i i bq a Po i 'f bei w anode circuit th mng rq ipfis hea 5e: Iifli vm a predetermined time relationship "to oscillatory signals insaid tuned anode circuit, pulse amplifying means coupled to said cathodeimpedance, the output signal of said pulse amplifying means comprisingone pulse in each of said pairs of pulses, phase shifting meanscoupled'to said tuned anode circuit and a nonlinear amplifying meanscoupled to said phase shifting means, said last-mentioned amplifyingmeans being adapted to produce a series of pulses having a,predetermined time relationship to the signal from said phase shiftingmeans, said lastmentioned series of pulses comprising a second pulse ineach of said pairs.

'7. A generator as in claim 6 wherein said phase shifting means isadjustable, the time spacing between pulses in each of said pairs beingdependent on the adjustment of said phase shifting means.

8. A generator for producing a series of marking pulses comprising anoscillator tube having at least an anode, a cathode and a control grid,a parallel inductor-capacitor circuit coupled between said anode and asource of anode potential, a resistor coupled between said cathode and apoint of reference potential, feedback means coupling said anode to saidgrid, frequency stabilizing means coupling said grid to said cathode, anauto-transformer having one ter minal thereof coupled to said point ofreference potential, a first capacitor coupled between said cathode andan intermediate tap on said autotransformer, and a serially connectedresistorcapacitor combination connected between said point of referencepotential and a second terminal of said auto-transformer, whereby thesignal appearing between the junction of said resistor-capacitorcombination and said point of reference potential is a series ofuniformly spaced pulses.

9. A generator for producing a series of marking pulses comprising anoscillator tube having at least an anode, a cathode and a control grid,a parallel inductor-capacitor circuit coupled between said anode and asource of anode potential, a resistor coupled between said cathode and apoint of reference potential, feedback means coupling said anode to saidgrid, frequency stabilizing means coupling said grid to said cathode, anauto-transformer having one terminal thereof coupled to said point ofreference potential, a first capacitor coupled between said cathode andan intermediate tap on said auto-transformer, a serially connectedresistor-capacitor combination connected between said point of referencepotential and a second terminal of said auto-transformer, saidresistor-capacitor combination and said auto transformer forming acritically damped circuit, a non-inverting amplifier means having theinput thereof coupled across the resistor of said resistor-capacitorcombination, the output signal of said amplifier comprising a series ofspaced pulses. V

10. A pulse generator as in claim 9, said pulse generator furthercomprising means coupling the output of said amplifier to said frequencystabilizing means thereby to increase the amplitude of said spacedpulses during the formation thereof.

ll. A generator for producing a series of pairs of marking pulses, saidgenerator comprising an oscillator tube having at least an anode, acathode and a control grid, a transformer having a primary and asecondary winding, said primary winding being coupled between said anodeand a source of anode potential, a resistor coupled between said cathodeand a point of reference potential, feedback means coupling said anodeto said grid, a first capacitor connected in shunt with said primarywinding for tuning said pri-' mary winding, an auto-transformer havingone terminal thereof coupled to said point of reference potential and anintermediate tap coupled to said cathode through a second capacitor, anamplifier having a, resistor-capacitor input circuit, said input circuitbeing connected across the winding of said auto-transformer, saidautotransformer and said input circuit constituting a critically dampedtuned circuit, said amplifier providing one series of marking pulses atthe output thereof, a resistor coupling a first terminal of saidsecondary winding to said anode, a second terminal of said secondarywinding being returned to a point of fixed potential, means for tuningsaid secondary winding, and a pulse forming amplifier coupled to saidfirst terminal of said secondary winding, the output of said pulseforming amplifier providing a second series of pulses, pulses of saidfirst and second series occurring in pairs, the spacing between saidpairs being a function of the relative resonant frequencies of the timedcircuits formed by saidprimary winding and said first capacitor and saidsecondary winding and said tuning means therefor.

ARDEN H. FREDRICK.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,226,459 Bingley Dec. 24, 19402,237,661 Ernst Apr. 8, 1941 2,397,150 Lyman Mar. 26, 1946 2,408,061Grieg Sept. 24, 1946 2,452,547

Chatterjea et al. Nov. 2, 1948

